A stent is a radially expandable endoprosthesis which is adapted to be implanted in a body lumen. Stents are typically used in the treatment of atherosclerotic stenosis in blood vessels and the like to reinforce body vessels and to prevent restenosis following angioplasty in the vascular system. They have also been implanted in urinary tracts and bile ducts and other bodily lumen. They may be self-expanding or expanded by an internal radial force, such as when mounted on a balloon.
Delivery and implantation of a stent is accomplished by disposing the stent about a distal portion of the catheter, percutaneously inserting the distal portion of the catheter in a bodily vessel, advancing the catheter in the bodily lumen to a desired location, expanding the stent and removing the catheter from the lumen. In the case of a balloon expandable stent, the stent is mounted about a balloon disposed on the catheter and expanded by inflating the balloon. The balloon may then be deflated and the catheter withdrawn. In the case of a self-expanding stent, the stent may be held in place on the catheter via a retractable sheath. When the stent is in a desired bodily location, the sheath may be withdrawn allowing the stent to self-expand.
In the past, stents have been generally tubular but have been composed of many configurations and have been made of many materials, including metals and plastic. Ordinary metals such as stainless steel have been used as have shape memory metals such as Nitinol and the like. Stents have also been made of biodegradable plastic materials. Stents have been formed from wire, tube stock, etc. Stents have also been made from sheets of material which are rolled.
A number of techniques have been suggested for the fabrication of stents from sheets and tubes. One such technique involves laser cutting a pattern into a sheet of material and rolling the sheet into a tube or directly laser cutting the desired pattern into a tube. Other techniques involve cutting a desired pattern into a sheet or a tube via chemical etching or electrical discharge machining.
Laser cutting of stents has been described in a number of publications including U.S. Pat. No. 5,780,807 to Saunders, U.S. Pat. No. 5,922,005 to Richter and U.S. Pat. No. 5,906,759 to Richter.
Most solid state lasers used for cutting purposes work in a free running regime. The typical temporal shape of a laser pulse is shown in FIG. 1. The laser pulse may be characterized as having three main parts. The most intense part of the pulse, labeled as B in FIG. 1, causes fast heating of a metal or other material within the laser beam, melting, splashing or evaporating the material which is useful for cutting. The initial part of the pulse, labeled as A and the tail end of the pulse, labeled as C, produce heating and melting of materials such as metals causing recrystallization of the metal and microcracks and is not as effective in cutting as the more intense portion of the beam. In order to reduce the formation of microcracks, it is desirable to condition the laser beam to transform the less intense portions of the beam into intense spikes of laser radiation.
All U.S. patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety.
Without limiting the scope of the invention a brief summary of the claimed embodiments of the invention is set forth below in accordance with 37 C.F.R. 1.73. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below.
A brief abstract of the technical disclosure in the specification is provided as well only for the purposes of complying with 37 C.F.R. 1.72. The abstract is not intended to be used for interpreting the scope of the claims.
The present invention in one embodiment is directed to a method of processing a stent preform comprising the steps of providing a stent preform and a laser system which outputs a laser beam, directing the laser beam at the stent preform and impinging the laser beam onto the stent preform to cut a desired pattern in the stent preform. The laser system used in accordance with the inventive method comprises a resonator cavity for resonating laser radiation, a gain medium contained in the resonator cavity and a pump for periodically pumping the gain medium. A radiation pulse is produced for each pump period. Each radiation pulse is conditioned to produce a pulse train of ordered pulses of radiation with each pulse train being output from the resonator cavity as an output laser beam.
In another embodiment, the invention is directed to a method of processing a stent preform comprising the steps of providing a stent preform and a laser system which outputs a laser beam, directing the laser beam at the stent preform and impinging the laser beam onto the stent preform to cut a desired pattern in the stent preform. The laser system used in accordance with the inventive method comprises an optical cavity for resonating laser radiation, a gain medium contained in the optical cavity and a pump for periodically pumping the gain medium. A radiation pulse is produced for each pump period. Each radiation pulse is conditioned to produce a pulse train of ordered pulses of radiation with each pulse train being output from the optical cavity as an output laser beam.
In another embodiment, the invention is directed to a method of manufacturing a stent comprising the steps of providing a stent preform in the form of a tube or a sheet and providing a laser system comprising an optical cavity for resonating laser radiation, an optical gain medium contained in the optical cavity and an optical pump for periodically pumping the optical gain medium. The laser system produces a radiation pulse for each pump period. The method further comprises the step of conditioning each radiation pulse to produce a pulse train of ordered pulses of radiation which are directed at the stent preform and impinged onto the stent preform to cut a desired pattern in the stent preform. Where the preform is a sheet, the sheet is then formed into a tube.
In another embodiment, the invention is directed to a method of treating a stent comprising the steps of providing a stent, providing a laser system comprising an optical cavity for resonating laser radiation, an optical gain medium contained in the optical cavity and an optical pump for periodically pumping the optical gain medium. The laser system produces a radiation pulse for each pump period. The method further comprises the step of conditioning each radiation pulse to produce a pulse train of ordered pulses of radiation. Each of the pulse trains is directed at desired portions of the stent and impinged onto desired portions of the stent. The pulse trains may be characterized by an amplitude, a pulse width, an inner train separation time between subsequent pulses in a pulse train, and an inter train separation time between subsequent pulse trains. In certain embodiments, the pulses may be conditioned using an electro-optical modulator which forms a part of feedback loop. The amplitude, pulse width, inner train separation time and inter train separation time are selected to polish, harden or engrave those portions of the stent impinged by the pulse trains.
In another embodiment, the invention is directed to a method of treating a workpiece comprising the steps of providing a workpiece and providing a laser system comprising an optical cavity for resonating laser radiation, an optical gain medium contained in the optical cavity and an optical pump for periodically pumping the optical gain medium. The laser system produces a radiation pulse for each pump period. Each radiation pulse is conditioned to produce a pulse train of ordered pulses of radiation, directed at desired portions of the workpiece and impinged onto desired portions of the workpiece. In certain embodiments, the pulses may be conditioned using an electro-optical modulator which forms a part of a feedback loop and the pulse trains may be characterized by an amplitude, a pulse width, an inner train separation time between subsequent pulses in a pulse train, and an inter train separation time between subsequent pulse trains. The amplitude, pulse width, inner train separation time and inter train separation time are selected to perform a treatment selected from the group consisting of engraving, hardening, cutting and polishing.
The invention is also directed to an image processing head for use with a laser. The head comprises a housing having a first opening therein for an input laser beam and a second opening therein for an output laser beam, a first mirror located within the housing, a second mirror located within the housing, a third mirror located within the housing and an optical path extender located within the housing. The first mirror redirects the input laser beam into the optical path extender. The second mirror redirects the laser beam from the optical path extender to the third mirror and the third mirror redirects the laser beam through the second opening in the housing.
Additional details and/or embodiments of the invention are discussed below.